SBS - The Best Value in QMS software

How to assess Process Capability for parallelism

C

Chris Skowron

#1
Here is a “real-life” example: There is a drawing specification for parallelism: 0.005”. The target is zero, the upper specification limit is 0.005”.

The manufacturing produces components with the actual parallelism 0.002” – 0.004”.

How to assess the capability of this process? What formulas should be used to calculate indices? What are the acceptability criteria?
 
Elsmar Forum Sponsor
A

Al Dyer

#2
Possibly use Cp which measures the spread of the process within the spec limits. Your not going to be centered (Cpk) with a one-sided spec. since yout spec is zero.

That is the conundrum of parallelism, the target is zero but under and over spec are the same thing, your either parallel or not.

Measurement gurus please!!!:)
 

Paul F. Jackson

Quite Involved in Discussions
#3
The orientation tolerance "parallelism" defines the size or width of the zone required to contain the axis, centerplane (of a feature of size), or points of a surface relative to the stated datum features.

There is only one answer per part. Even though points on the surface are infinately displaced, it is the width of the zone that is required to contain them that will be examined statistically.

For capability (assuming process in-control) compare the mean of those zone widths and their associated distribution to the Upper Specification Limit.
 
F

fyu111 - 2005

#4
CpK - Rememeber that the Zmin lowest is the true cpk if you calculate it to the upper spec it should qualify. Some software programs allow you to input one sided tolerance. Regardless, usually with parallelism all you care about to the tolerance is approaching the max. 0 would be perfectly parallel and the optimum.
 
D

Dave Dunn

#5
Agreeing with fyu111, Cpk would be appropriate, caculating only for Zupper since it is a one-sided specification.

One question about your data: does your measurement method resolve just to increments of .001" or can it accurately display finer increments? If only .001" your capability calculation might not give you a very clear picture since your number of discreet categories would be limited (0, .001, .002, .003, .004, .005)
 
D

Darius

#6
Beware on one specs. Cpk doesn't has a good behabiur on "one specs" at least if you care more about being on target than with lower variation. Cpmk can be more helpfull because the target is included and in Cpk the other limit is implicitelly added (you are taking it as it is a simetrical leap around the mean and the "not included" spec limit at the same distance from the mean that the other, but didn't noticed - the only way to have the same value).

Just playing with numbers but if you have a time series with
average of 104.7148
stadard deviation of 2.957962
Upper Spec 115
so .... your Cpk is 1.159042

if you take the lower Spec as average - ( Upper Spec - average)
So ... your virtual lower spec is 94.42959
and .. your Cpk for the lower bound is 1.159042
:magic:

:mg:
 
C

cyberspider

#7
An idea

I think you may use mean sqare error or Taguchi's loss function here straight way. Use the letter one to appreciate what is the deviation.

If not clear pl. post reply for this..
 
A

Arvind

#8
Parallelism data is non-normal in most cases in real life

It is a well known fact that most cases of parallelism or out of roundness data is not normal. In such cases, you cannot assume normality assumption and calculate capability.

In addition, you have only one sided (upper) specification. You may use Weibull analysis to fit the data. It will tell you DPMO exceeding the upper specification.
 

Jim Wynne

Staff member
Admin
#9
Arvind said:
It is a well known fact that most cases of parallelism or out of roundness data is not normal. In such cases, you cannot assume normality assumption and calculate capability.
Sorry, Arvind, but this doesn't make sense. How can you assume lack of normality? What if an entire lot of say, 1000 units is made, and the same parallelism error is present in all of them? (I've seen it happen; all it requires is careless setup and failure to check the feature until it's too late.) Of course, one should never assume normality when calculating Cpk, but out-of-spec isn't always equal to non-normal.

Arvind said:
You may use Weibull analysis to fit the data. It will tell you DPMO exceeding the upper specification.
No, it will allow you to estimate PPM out of specification, not necessarily DPMO, although there's no good reason to invoke "millions" when you're not actually making a million of something.
 
Thread starter Similar threads Forum Replies Date
V How to Assess Process Capability at the Development or Optimization Phase Capability, Accuracy and Stability - Processes, Machines, etc. 6
A Cnpk (Non-Parametric Capability Analysis) to assess whether the Process is Stable Capability, Accuracy and Stability - Processes, Machines, etc. 7
D Minimum number of Subgroups to assess Process Capability Statistical Analysis Tools, Techniques and SPC 3
T Method to assess Measurement System of a Continuous Process Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
R CQI-15 Welding System Assess. & CQI-17 Special Process: Soldering Various Other Specifications, Standards, and related Requirements 6
Q Maintenance Process Audit Check List to Assess Maintenance Process ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
MrTetris How to qualitatively assess initial probability ISO 14971 - Medical Device Risk Management 4
E ISO 13485 7.6 Control of monitoring and measuring equipment - Assess the Validity ISO 13485:2016 - Medical Device Quality Management Systems 4
B How to assess which directives and standards apply - Brewing and distilling products CE Marking (Conformité Européene) / CB Scheme 1
S Medical Device Changes and How to Assess Their Impacts to Essential Requirements EU Medical Device Regulations 2
Ronen E Independence on Notified Bodies, inter alia of Manufacturers they Assess EU Medical Device Regulations 7
M BS 10008:2014 Registration - UKAS accredited company in the UK to assess our company IEC 27001 - Information Security Management Systems (ISMS) 4
G How to assess Customer Satisfaction without using surveys ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 14
L How to Assess Adhesion of Stickers on Painted Steel Manufacturing and Related Processes 5
S Required to Assess and Evaluate all Suppliers? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 1
R How to assess capability for parameters which has got either Min values or Max values Statistical Analysis Tools, Techniques and SPC 2
V Criteria used to assess the Validity of a Complaint - Insurance Company Customer Complaints 4
somashekar Non Moving Electronic components - How to assess its fitness for use. Manufacturing and Related Processes 3
B GM's QSB - Requirement, Checklists needed - Checklist used by GM to assess & sample Customer and Company Specific Requirements 9
S Advice on how to assess competency in the absence of academic qualifications? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 24
Z How to implement "assess" mentioned in the clause 7.1.4? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
B Designing a Test Part to Assess CMM Operator's Knowledge Design and Development of Products and Processes 9
M Method to assess / calculate a design wrt DFM/DFA - Seeking template Design and Development of Products and Processes 4
B How to sufficiently self-assess a QM (Quality Management) system? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
P How to Assess the Effectiveness of the QMS (Quality Management System) ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
apestate Assess effects of MT&E found out of tolerance - ISO9001 Section 7.6 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
K What are You doing to assess Customer Satisfaction? Please help! ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 24
S 17025 Flexible Scopes of Accreditation - Laboratory to 'self-assess' new test method ISO 17025 related Discussions 2
M Ford QOS - 3rd Party Auditing body able to assess the QOS Assessment? QS-9000 - American Automotive Manufacturers Standard 1
DuncanGibbons Process flow & PFMEA for production planning and simulation activities? Process Maps, Process Mapping and Turtle Diagrams 7
N Help with understanding Process Controls Manufacturing and Related Processes 4
M VDA 6.3 – Workshop for Certified Process Auditor VDA Standards - Germany's Automotive Standards 1
C Process Consistency Manufacturing and Related Processes 5
I PFD (Process Flow Diagram) approach. Setup details as part of PFD? Manufacturing and Related Processes 3
K Business Process Flowchart Process Maps, Process Mapping and Turtle Diagrams 2
L Looking for Control Plan and FMEA Stamping process FMEA and Control Plans 2
J License renewal process in Iran Other Medical Device Regulations World-Wide 0
J Definition Outsourced process - Clear definition - 13485 Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 5
S IS0 13485 process flows ISO 13485:2016 - Medical Device Quality Management Systems 2
H Verification Process for the existing MDS Product IEC 62304 - Medical Device Software Life Cycle Processes 5
C Revalidation of Process Equipment for Equipment Transfered to New Facility. ISO 13485:2016 - Medical Device Quality Management Systems 5
Q Process map Evaluation and Analysis Method Process Maps, Process Mapping and Turtle Diagrams 5
S In process inspection Manufacturing and Related Processes 2
S Brexit 100% inspection during in process inspection Manufacturing and Related Processes 11
A Complaint review as part of the complaint handling process? ISO 13485:2016 - Medical Device Quality Management Systems 3
mustomutlu Process Validation Final Report Other Medical Device and Orthopedic Related Topics 2
Q Process Matrix_Audit Matrix Quality Management System (QMS) Manuals 4
Q Process description for outsourced processes ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
Q Process matrix examples of ISO 9001 & 14001 ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 2
J Need Help with FPY Data in Assembly Process Manufacturing and Related Processes 7

Similar threads

Top Bottom